1. Field of the Invention
The present invention relates to inertial rate sensors and more particularly to vibratory rate of turn devices, particularly for aircraft or other maneuverable vehicles, employing force feed back or self-nulling techniques for maintaining motion of the vibratory element in a predetermined plane, the force so required being proportional to a turn rate tending to cause vibration out of that plane.
2. Background of the Invention
The principal examples of prior art vibratory rate of turn devices for craft stabilization and navigation purposes are found in the J. Lyman, E. Norden U.S. Reissue Pat. No. 22,409, dated Dec. 21, 1943 and assigned to Sperry Rand Corporation, a reissue of the U.S. Pat. No. 2,309,853, originally issued Feb. 21, 1943. The present invention is a basic improvement over various embodiments of the reissue patent, all of which operate in an open-loop manner and therefore are subject to the inconsistancies and errors associated with most open loop types of sensors, such as drift, scale factor change, temperature sensitivity, output signal non-linearity, et cetera. The present invention utilizes closed loop techniques and embodies the known characteristics of piezoelectric devices for imparting vibration forces to the sensing element. However, in its broadest aspects, the present invention is applicable to the general class of vibratory sensing devices.
In general with respect to such piezoelectric transducers, operation is based upon electrical-charge, mechanical-strain phenomenon in the material, usually referred to in terms of coupling coefficients, when vibrated to develop linear momentum in a sensory mass. In open loop sensors which use the high resolution of this energy conversion mechanism, the drift and scale factor characteristics are directly dependent upon the stability and characteristics of the piezoelectric material coupling coefficient. Thus, use of such transducers in inertial instruments has been hampered by drift in stability and scale factor, only to be overcome to a degree in the past by intensive development of more stable piezoelectric materials. But other troublesome areas have also been recognized and overcome by the present invention; these include the need to reduce cross-coupling effects at zero rate of turn, temperature sensitivity, nodal point mislocation effects, non-symmetrical motion of the sensor, and electrode non-symmetries.